Some known load transfer devices suffer from the drawback that they are incapable of negotiating the intermediate brackets along the elongate support element. One solution to this problem is to provide special brackets which can be "opened" to allow the supported load to pass. The weakness of this approach is that the elongate support element temporarily lacks support at the very point where the installer thought it necessary and at the precise moment when it is most needed. Another likely problem is that the brackets may not be accessible to the system user.
An alternative solution is to employ special entry/exit fittings or access points along the elongate support element so that the load transfer device can be attached and removed. The drawback of this proposal is that the access points are not always conveniently situated in relation to the exact location at which attachment or removal is desired. Improved load transfer devices have been developed which are capable of automatically traversing intermediate brackets for the elongate support element without user intervention. Such devices typically comprise a pair of rotatable wheels having a series of recesses at spaced locations around their peripheries, the adjacent recesses being separated by a radially projecting part of the wheel. A cooperating slipper part is mounted on the wheels by means of formations which inter-engage with complementary formations on the radially projecting wheel parts. A space between the slipper part and the wheels is dimensioned to receive elongate support element such as a cable or a rigid elongate element.
In use, the device is able to negotiate intermediate brackets for the elongate support element without user intervention by accommodating the bracket legs in a pair of aligned recesses carried by the respective wheels. Rotation of the wheels relative to the slipper part causes the intermediate bracket to pass behind the slipper part, in the aligned recesses of the rotating wheels.
Unfortunately, such devices still fail to address the problem of ease of attachment to or removal from the elongate support element.
A removable load transfer device is known from U.S. Pat. No. 5,245,931. This device has a specially-configured oblique cut-out portion formed in each of its rotating wheels to facilitate removal from and attachment to a safety line or cable. In order to effect such removal or attachment, the wheels must be aligned so that the safety line or cable can be accommodated in the cut-outs at an oblique orientation relative to the axis of rotation of the wheels. This enables the safety line or cable to be passed behind the slipper part. One disadvantage of this device is that it requires precise alignment of a number of parts and is therefore awkward to use. Also, the necessity to orient the device obliquely in relation to the safety line or cable means that considerable clearance is required around the device in order to remove or attach it.
Another disadvantage of the prior art device referred to above is that it does not fail safe. Although locking means are optionally provided to prevent inadvertent alignment of the cut-outs leading to unwanted disengagement from the safety line or cable, there is nothing to prohibit deactivation of the locking means. Nor is there anything to ensure that the locking means are actuated in the first instance. Thus, it is possible for a user to install the device on the safety line or cable without positively actuating the locking means.